Synthesis of crown-ether precocenes

Preparation of potential insect antijuvenile hormone agents with 15-crown-5 and 18-crown-6 moieties connecting the C-6 and C-7 positions of the 2 H-chromene ring of precocenes is described.     

Thickness–concentration–viscosity relationships in spin-coated metalorganic ceria films containing polyvinylpyrrolidone

Zr-doped ceria thin films were prepared by spin-coating metalorganic solutions containing polyvinylpyrrolidone (PVP), which serves as a relaxing agent to relieve the strong mechanical stresses developed during the thermal decomposition step. The precursor solutions were deposited on silicon substrates and subsequently heated in air at 500 °C. The complete decomposition of organics was checked by infrared spectroscopy with attenuated total reflectance. The molar ratio between PVP and total metal ions was varied between zero and one. Furthermore, the effect of using two different PVP molecular weights was also investigated. For the high molecular weight of PVP, crack-free films as high as 150 nm could be obtained compared to 30 nm when no PVP is added. Thickness after spin-coating and after thermal decomposition were determined by profilometry and correlated with the polymer concentration in the precursor solution, showing a linear dependence with PVP concentration in both cases. The main controlling parameter of the final thickness is the viscosity, with similar power law dependencies both before and after thermal treatment, which would indicate that the porosity fraction remains essentially constant in the final films. Furthermore, AFM analysis was used to investigate the flatness and surface porosity of the films after the thermal treatment.     

Action de l'anhydride acétique sur les (aziridinyl-1)-2 tétra-hydropyrannes et sur les dialkylamino-2 tétrahydropyrannes: Influence des substituants de l'azote sur l'orientation de la réaction

The 2-(1-aziridinyl)tetrahydropyrans cannot be obtained by aminolysis of the 2-dialkylaminotetrahydropyrans. These compounds are synthesized by the Hofmann reaction between 2-chlorotetrahydropyrans and ethylenimine. The effect of acetic anhydride on the 2-(1-aziridinyl) and 2-dialkylaminotetrahydropyrans was studied. The 2-dimethylaminotetrahydropyrans were converted into 2-acetoxytetrahydropyrans and dimethylacetamide by cleavage of the carbon-nitrogen bond. Ring opening of the oxygen heterocycle gives the corresponding dialkylacetamides and polymerised products. The 2-(1-aziridinyl)tetrahydropyrans allow the synthesis of the N-(2-tetrahydropyrannyl)-N-(2-acetoxy-ethyl)acetamides. Acetic anhydride ring opens the nitrogen heterocycle.     

Identification of substituted sites on MUC5AC mucin motif peptides after enzymatic O-glycosylation combining beta-elimination and fixed-charge derivatization.

A strategy for determination of O-glycosylation site(s) in glycopeptides has been developed using model compounds obtained by enzymatic glycosylation (by human GaNTase-T2 isoform) on peptides derived from the human MUC5AC mucin tandem repeat motif. The beta-elimination-addition reaction (using dimethylamine and concomitantly ethanethiol) on the formerly glycosylated sites through a Michael-type condensation produced efficient deglycosylation with appropriate chemical modification. After N-terminal derivatization by a phosphonium group, peptide sequencing was then carried out by nanospray tandem mass spectrometry experiments. The highly predictable fragmentation pathways of these fixed-charge phosphonium derivatives enable straightforward recognition of glycosylation site(s) based on the mass increment of +44 Da for originally glycosylated threonine compared to the mass of fragments containing nonglycosylated residues.     

Reduction of cyclic group 6 Fischer carbene complexes: a case of exquisite regioselectivity

The reduction of alpha,beta-unsaturated cyclic group 6 metal-carbene complexes strongly depends on the electronic profile of the groups attached both to the carbene and the beta-carbon and occurs with exquisite regioselectivity. Thus, for complexes 8 the reduction does not take place at the carbene carbon but exclusively at the gamma-carbonyl group. The resulting alkoxide 20 evolves to a tricyclic epoxide structure 21, which precludes additional hydride transfers. Complex 9 experiences the exclusive 1,4-reduction because of the imino character of the beta-carbon (due to the participation of the aromatic resonance form 22). In contrast, monocyclic carbene complexes 10 behave as their acyclic congeners and experience 1,2-hydride addition followed by the 1,3-migration of the metal center. In this case, the participation of eta(3)-Cr(CO)(5) species 31 allows us to understand the labeling pattern found in the final products.     

DFT characterization of adsorbed NH(x) species on Pt(100) and Pt(111) surfaces

Periodic density functional theory (DFT) calculations using plane waves have been performed to systematically investigate the adsorption and relative stability of ammonia and its dehydrogenated species on Pt(111) and Pt(100) surfaces. Different adsorption geometries and positions have been studied, and in each case, the equilibrium configuration has been determined by relaxation of the system. The vibrational spectra of the various ammonia fragments have been computed, and band assignments have been compared in detail with available experimental data. The adsorption of NH3 (on top) and NH2 (bridge) is more favorable on Pt(100) than on Pt(111), while similar adsorption energies were computed for NH (hollow) and N (hollow) on both surfaces. The remarkably lower adsorption energy of NH2 over Pt(111) as compared with Pt(100) (the difference being approximately 0.7 eV) can be related to different geometric and electronic factors associated with this particular intermediate. Accordingly, the type of platinum surface determines the most stable NH(x) fragment: Pt(100) has more affinity for NH2 species, whereas NH species are preferred over Pt(111).     

Kinetics of appearance of hemorphins from bovine hemoglobin peptic hydrolysates by a direct coupling of reversed-phase high-performance liquid chromatography and electrospray ionization mass spectrometry

Reversed-phase high-performance liquid chromatography coupled with electrospray ionization mass spectrometry was used to improve the preparation of three opioid peptides (Leu-Val-Val-hemorphin-7, Val-Val-hemorphin-7 and Val-Val-hemorphin-4) resulting from bovine hemoglobin peptic hydrolysates. Optimal conditions for the preparation of these peptides were determined thanks to their kinetic studies of appearance in the course of peptic hydrolyses as a function of degree of hydrolysis of hemoglobin. We propose a low degree of hydrolysis (3%) to prepare Leu-Val-Val-hemorphin-7, a mean degree of hydrolysis (11%) to prepare Val-Val-hemorphin-7 and a high degree of hydrolysis (21%) to prepare Val-Val-hemorphin-4.